The present invention relates to a surgical microscopy system having an optical coherence tomography (OCT) facility. In particular, the present invention relates to a surgical microscopy system having an OCT facility, wherein a beam of measuring light is scanned across an object to be analyzed by the OCT facility.
An OCT system is for example known from EP 0 697 611 A2. A broad-band OCT-light source generates OCT-measuring light comprising different wavelengths within a certain bandwidth. A principal wavelength generated by the OCT-light source and the bandwidth of the OCT-light source determine the coherence length of the OCT-measuring light. There is a reciprocal relationship between the bandwidth of the OCT-light source and the coherence length of the OCT-measuring light generated by the OCT-light source. Two different parts of the OCT-measuring light can interferometrically only be superimposed, if a difference of optical path lengths traversed by the two different parts of OCT-measuring light is smaller than the coherence length of the OCT-light source.
Typically, a first part of the OCT-measuring light is reflected by a reference surface, such as a plane mirror, to traverse a controllable optical path length. The second part of the OCT-measuring light is directed to an object to be investigated and is reflected at regions in different depths of the object. Thus, this second part of the OCT-measuring light reflected at the object is comprised of a number of OCT-measuring light portions that have traversed different optical path lengths depending on the depth of the region of the object at which they were reflected.
In time domain OCT the reference surface is displaced, for example using a continuous movement or in a stepwise manner, such that the different OCT-measuring light portions reflected from the object interferometrically superimpose with the first part of the OCT-measuring light reflected by the reference surface at positions of the reference surface, where the OCT-measuring light portions reflected from the object have traversed an optical path length substantially equal to the optical path length traversed by the reflected first part of the OCT-measuring light. This allows to gain structural information of the object in an axial (i.e. depth) direction defined by the direction of incidence of the OCT-measuring light at the object.
To obtain structural information along an axial direction not only at a single point of the object, the second part of the OCT-measuring light needs to be scanned across a laterally extended region at the object. To achieve this, typically a scanning system is utilized including for example two mirrors spaced apart that are rotatable about axes perpendicular to each other. Thereby it is possible, to obtain a three-dimensional representation of a volume portion of the object below the surface of the object. This three-dimensional representation is in particular valuable for a surgeon to locate structure portions within the volume of the object to be manipulated, in particular useful during opthalmologic surgeries. These surgeries may be directed to regions of an anterior portion of the eye or may be directed to regions of a posterior portion of the eye. In particular, imaging the cornea by OCT and adjacent regions or imaging the retina by OCT have found widespread demand during opthalmologic surgeries.
An optical microscopy system includes an objective lens and an ocular system to image an illuminated region of an object. For this, a user may look through the ocular system to directly image the object region to his or her retina, or may look at an image acquired by a CCD camera. A CCD acquired image may be displayed to a desk monitor or may be displayed for example to a head-mounted display. In a number of known optical microscopy systems the beam path of the system is parallel downstream of the objective lens. This allows in a simple way to provide a stereoscopic optical microscopy system, wherein light emanated from the object under slightly different angles is guided downstream the objective lens to two tubular bodies harboring two oculars for the left and the right eye of the observer. Thereby, an enlarged stereoscopic imaging of the object is possible. A stereoscopic optical microscopy turns out to be indispensable for opthalmologic surgeries.
It is known for example from EP 0 697 611 A2 to combine an optical microscopy system with an OCT system. In this system, the light beam of the OCT system traverses the objective lens of the optical microscopy system. However, in this system it is difficult to arrange a reflector which deflects the OCT-measuring light beam of the OCT system in order to guide it to and traverse the objective lens of the optical microscopy system, thus to be incident on the object without impairing the performance of the optical microscopy system.
An object of the present invention is to provide a microscopy system that integrates an optical microscopy system and an OCT system that reduces the disadvantages of the prior art mentioned above.
It is a further object of the present invention to provide a microscopy system combining an optical microscopy system and an OCT system, wherein a capability and performance of the optical microscopy system is not impaired by the presence of the OCT system and vice versa.
It is a further object of the present invention to provide an optical system enabling microscopic examination, OCT and measurement of a wavefront of wavefront measuring light returned from an object.
An even further object of the present invention is to provide a surgical microscopy system particularly suitable for opthalmologic surgeries.